Uric acid as well as its salt and derivative (hereinafter they are simply referred to as "uric acid" altogether) are used in various cosmetic compositions as a substrate of one of oxidases, uricase, a stabilizer of a moisturizer, an ingredient for preventing skin roughness, an antidandruff ingredient and the like. For example, JP 61-118312 A discloses a keratin fiber dyeing composition of pH 4 to 10.5 which comprises uric acid, an ampholytic surfactant, a thickener and the like and a method for dyeing keratin fiber using the composition. JP 61-183204 A discloses a cosmetic composition comprising a moisturizer and uric acid as a stabilizer for the moisturizer. JP 63-246313 A (U.S. Pat. No. 4,961,925) discloses a hair cosmetic composition of pH 7.5 to 8.5 which comprises dielectron reducing oxidase, uric acid as a donor of the enzyme and the like. JP 1-275511 A discloses a topical composition for skin external use containing uric acid for preventing skin roughness. JP 1-275516 A discloses an antidandruff composition containing uric acid. JP 8-217652 (EP 0716846 A) discloses an oxidation hair dyeing composition of pH 6.7 to 9.5 which comprises uric acid, potassium hydroxide and/or monoethanolamine and the like.
On the other hand, since the water-solubility of uric acid is very low such as about 0.0067%, at present, only a small amount of uric acid can be used in case of an aqueous solubilized system. In addition, in case of a dispersion system wherein uric acid is added in excess of its solubility, there are many problems such as precipitation of uric acid, limitation of containers to be used for packaging end products due to clogging of orifices thereof and the like.
Moreover, although uric acid can be solubilized in water to a certain extent by appropriately choosing an alkali, mere solubilization is insufficient for practical use due to such problems as drip and less fitness for hair or skin upon application, and the like. Then, in practice, it is necessary to add surfactants and polymers in view of usability.
However, in aqueous cosmetic compositions containing surfactants and polymers, no satisfactory technique for stably solubilizing uric acid has yet been found.